What Counts as a Primary Source?
A primary source is a statement of law issued by a body with the authority to make law. There are four kinds: constitutions (federal and state), statutes enacted by legislatures, regulations issued by agencies under statutory authority, and court opinions — the case law explained in our case law guide. Local ordinances and court rules belong to the family too. What unites them: a court can be obligated to follow them. When your research question is “what is the law,” only these sources are the answer, and our guide to finding statutes and codes covers where the enacted ones live.
What Counts as a Secondary Source?
A secondary source explains, organizes, or criticizes the law without being law. The main genres, roughly from most to least authoritative in courts’ eyes: Restatements of the Law (the American Law Institute’s systematic formulations, which courts quote so often that some sections function almost like rules — but remain secondary); treatises, the multi-volume expert works on a field; law review articles, scholarly analysis often cited for novel questions; practice guides written for working lawyers; and legal encyclopedias (American Jurisprudence, Corpus Juris Secundum) for broad orientation. One more category deserves its own warning: headnotes, case summaries, and database annotations are editorial work product — not even secondary authority. They are finding tools, and citing them is a classic beginner error.
Binding vs Persuasive Authority
The primary/secondary line crosses a second one: binding versus persuasive. All secondary sources are at most persuasive. Primary sources are binding only within their scope — a Texas statute binds no one in Ohio, and a Ninth Circuit opinion does not bind the Fifth. So authority sorts into three tiers: (1) binding primary — your jurisdiction’s constitution, statutes, regulations, and higher-court decisions; (2) persuasive primary — other jurisdictions’ law, and dicta or lower-court decisions from your own; (3) persuasive secondary — everything written about the law. Research aims at tier one; tiers two and three fill gaps and supply reasoning when tier one runs out. How binding hierarchy works inside case law — stare decisis, holdings versus dicta — is covered in what case law is.
When to Use Secondary Sources First
Read secondary first; cite primary. That paradox is the core of efficient research method. Starting an unfamiliar question in primary sources means keyword fishing in an ocean of opinions; starting with a treatise section or encyclopedia entry gives you the framework, the vocabulary courts use, and citations to the leading authorities — which you then read, update, and cite. Secondary sources are also the honest shortcut for a field’s structure: a researcher who reads one good overview knows which three issues matter before opening a single case. The step-two role they play in the research process is laid out in how to do legal research. When is citing a secondary source appropriate? When no primary authority exists on your point, when a Restatement section is itself the rule your jurisdiction has adopted, or when you need a scholar’s synthesis for a novel argument.
The Cheat Table
| Source | Primary or secondary | Authority | How to use it |
|---|---|---|---|
| Constitution | Primary | Binding — supreme within its jurisdiction | Cite directly |
| Statute / code section | Primary | Binding in its jurisdiction | Cite directly; check for amendments |
| Regulation (e.g., CFR) | Primary | Binding if validly issued | Cite directly |
| Court opinion (your jurisdiction, higher court) | Primary | Binding | Cite directly; citator-check |
| Court opinion (other jurisdiction) | Primary | Persuasive | Cite when no binding authority |
| Restatement | Secondary | Persuasive (often highly) | Cite when courts in your state follow it |
| Treatise / practice guide | Secondary | Persuasive | Background; cite sparingly |
| Law review article | Secondary | Persuasive | Background; cite for novel arguments |
| Legal encyclopedia (Am Jur, CJS) | Secondary | Weakly persuasive | Orientation; rarely cite |
| Headnotes / annotations | Neither (editorial) | None | Finding tools only — never cite |
Pin this next to one more rule and you have the whole discipline: whatever you cite, verify it first — statutes for amendment, cases through a citator.